1. Field of the Invention
The present invention relates to a malfunction detection device for a resolver, which outputs a sine signal representative of sin θ and a cosine signal representative of cos θ according to a rotation angle θ of a rotating body.
2. Description of the Related Art
One of malfunction detection devices for a resolver of this type has been proposed in, for example, JP-A-9-72758 (refer to paragraph [0020] and FIG. 5). In the malfunction detection device for a resolver disclosed in JP-A-9-72758, a value of sin2 θ+cos2 θ is calculated on the basis of the sine signal and the cosine signal, and when a calculated value falls outside a given normal range, it is determined that malfunction occurs within the resolver.
However, when malfunction occurs in the resolver, the value of sin2 θ+cos2 θ (the sum of squares) may be varied between inside and outside of the above normal range according to the rotation angle θ of the rotating body. In this case, since a state in which the value of sin2 θ+cos2 θ falls outside the normal range is not continued, even if malfunction occurs in the resolver, the malfunction may not be surely detected. In addition, even if the resolver is normal, because the value of sin2 θ+cos2 θ may temporarily fall outside the normal range due to an influence of noise, for example, the normal resolver may be determined as fault.